Surfactant mixtures microemulsions

When comparable amounts of oil and water are mixed with surfactant a bicontinuous, isotropic phase is formed [6]. This bicontinuous phase, called a microemulsion, can coexist with oil- and water-rich phases [7,1]. The range of order in microemulsions is comparable to the typical length of the structure (domain size). When the strength of the surfactant (a length of the hydrocarbon chain, or a size of the polar head) and/or its concentration are large enough, the microemulsion undergoes a transition to ordered phases. One of them is the lamellar phase with a periodic stack of internal surfaces parallel to each other. In binary water-surfactant mixtures, or in... 

A. Ciach. Statistical mechanics of ternary surfactant mixtures including microemulsions. Pol J Chem 66 1347-1387, 1992. 

K. Chen, C. Ebner, C. Jayaprakash, R. Pandit. Microemulsions in oil-water-surfactant mixtures Systematics of a lattice-gas model. Phys Rev A 55 6240, 1988. 

A. Ciach, J. S. Hoye, G. Stell. Microscopic model for microemulsion. II. Behavior at low temperatures and critical point. J Chem Phys 90 1222-1228, 1989. A. Ciach. Phase diagram and structure of the bicontinuous phase in a three dimensional lattice model for oil-water-surfactant mixtures. J Chem Phys 95 1399-1408, 1992. 

Different methods are used in microemulsion formation a low-energy emulsification method by dilution of an oil surfactant mixture with water and dilution of a water-surfactant mixture with oil and mixing all the components together in the final composition. These methods involve the spontaneous formation of microemulsions and the order of ingredient addition may determine the formation of the microemulsion. Such applications have been performed with lutein and lutein esters. ... 

High pressure homogenization may also be used to form microemulsions but the process of emulsification is generally inefficient (due to the dissipation of heat) and extremely limited as the water-oil-surfactant mixture may be highly viscous prior to microemulsion formation. ... 

Graciaa A. et alii, The Partitioning of Nonionic and Anionic Surfactant Mixtures Between Oil/Microemulsion/Water Phases , n° SPE 13 030, Houston, 1984. 

Oil-water mixture is added to a surfactant. To this emulsion, a short-chain alcohol (with four to six carbon atoms) is added continuously until a clear mixture (microemulsion) is obtained. Microemulsions will exhibit very special properties, quite different from those exhibited by ordinary emulsions the microdrops may be considered as large micelles. 

The partitioning can be revealed by different patterns that are found in experimental data. The first one is a reduction in solubilization because a part of the surfactant mixture is no longer at interface. For the same amount of surfactant in the system at optimum formulation, the volume of microemul-son middle phase is lower, just because a certain proportion of the surfactant is no longer in the microemulsion, but has partitioned into one of the excess phases. However, it is worth noting that there are other reasons for the solubilization to decrease, hence this is only a hint. 

Upadhyaya A, Acosta EJ, Scamehorn JF, Sabatini DA (2006) Microemulsion phase behavior of anionic-cationic surfactant mixtures Effet of tail branching. J Surfact Deterg 9 169-179... 

There are a number o-f processes which have not been discussed (because o-f space) in which mixture o-f sur-f actants are important. Among these are foaming, emulsion formation, liquid crystal formation, microemulsion formation, adsorption as 1iquid—1iquid interfaces, and phase partitioning of surfactants between immiscible liquid phases. These areas will also see increased interest in the use of surfactant mixtures. 

The above-mentioned artificial microbubble surfactant mixtures, and other successful mixtures found for stable microbubble production (ref. 544-546), all contain saturated glycerides (with acyl chain lengths greater than 10 carbons) combined with cholesterol and cholesterol derivatives (cf. Chapters 9 and 10, and ref. 544). As described earlier, long chain lengths in nonionic (or even unionized) surfactants are known to favor the formation of both large, rodlike micelles (as opposed to small spherical micelles) and macroemulsions (as opposed to microemulsions) (see... 

Rabagliati et al. (14) studied the polymerization of styrene in a three phase system containing an anionic-nonionic surfactant mixture and brine. Both AIBN and potassium persulfate initiators were used. The system was reported to be microemulsion continuous and even multicontinuous. (14). No autoacceleration was observed and the authors concluded that the polymerization exhibits an inverse dependence of the degree of polymerization on initiator concentration, similar to bulk solution polymerization. 

At room temperature, the microemulsion is single phase and balanced when the wt. X of the hydrophile is 67 X of the total surfactant mixture. At higher concentrations of the hydrophile, the system splits into two phases a lower mlcroemulslon phase in equilibrium with excess oil. The first manifestation of the phase separation results in a cloudy solution which can be generated by either a change in the H/L properties or by increasing the temperature. It should be realized that the temperature response of anionic surfactants and microemulsions is opposite to that of... 

Fig. 5 Ternary phase diagram for oil, water, and surfactant mixtures showing micellar, microemulsion, and multiphase macroemulsion regions with schematic representations of various structures.

The most common definition of a microemulsion characterises it as a thermodynamically stable, transparent, optically isotropic, freely flowing surfactant mixture, often containing co-surfactants (e.g. alcohol) and added salts [37]. We restrict the definition further to non-crystalline (disordered) aggregates, since crystalline isotropic phases are better considered as liquid crystalline mesophases. Indeed, the most succinct description of a microemulsion would involve its microstructure. However, this has proven to be a very equivocal issue. So much so that until very recently it was widely believed that microemulsions were devoid of microstructure hence the thermod)mamic definition. 

But some double-chain cationic surfactants form microemulsions when mixed with only water and oil over a large region of the ternary phase triangle [38, 39]. These surfactants are virtually insoluble in both water and oil and therefore are located exclusively at the oil-water interface. This aids structural analyses significantly. We shall focus on mixtures containing DDAB. Some typical phase diagrams for these mixtures are reproduced in Fig. 4.19. 

A significant number of patents on LDLDs have been issued in the U.S., Europe, and Japan in recent years. Listed in Table 7.10 are examples of LDLD patents formulating for effective soil removal/cleaning. The technology utilized in these patents ranges from special surfactants, surfactant mixtures, salts, and microemulsion to the use of special additives such as lemon juice and abrasives. 

The extensive research on microemulsions was prompted by two oil crises in 1973 and 1979, respectively. To optimise oil recovery, the oil reservoirs were flooded with a water-surfactant mixture. Oil entrapped in the rock pores can thus be removed easily as a microemulsion with an ultra-low interfacial tension is formed in the pores (see Section 10.2 in Chapter 10). Obviously, this method of tertiary oil recovery requires some understanding of the phase behaviour and interfacial tensions of mixtures of water/salt, crude oil and surfactant [4]. These in-depth studies were carried out in the 1970s and 1980s, yielding very precise insights into the phase behaviour of microemulsions stabilised by non-ionic [5, 6] and ionic surfactants [7-9] and mixtures thereof [10]. The influence of additives, like hydro- and lyotropic salts [11], short- and medium-chain alcohols (co-surfactant) [12] on both non-ionic [13] and ionic microemulsions [14] was also studied in detail. The most striking and relevant property of micro emulsions in technical applications is the low or even ultra-low interfacial tension between the water excess phase and the oil excess phase in the presence of a microemulsion phase. The dependence of the interfacial tension on salt [15], the alcohol concentration [16] and temperature [17] as well as its interrelation with the phase behaviour [18, 19] can be regarded as well understood. 

From the late 1980s onwards, the research on microemulsions turned to the understanding of the fascinating microstructure of these mixtures. Microemulsions are created by a surfactant film forming at the microscopic water/oil interface. Different methods such as NMR self-diffusion [20, 21], transmission electron microscopy (TEM) [20, 22]... 

Ionic surfactants with only one alkyl chain are generally extremely hydrophilic so that strongly curved and thus almost empty micelles are formed in ternary water-oil-ionic surfactant mixtures. The addition of an electrolyte to these mixtures results in a decrease of the mean curvature of the amphiphilic film. However, this electrolyte addition does not suffice to drive the system through the phase inversion. Thus, a rather hydrophobic cosurfactant has to be added to invert the structure from oil-in-water to water-in-oil [7, 66]. In order to study these complex quinary mixtures of water/electrolyte (brine)-oil-ionic surfactant-non-ionic co-surfactant, brine is considered as one component. As was the case for the quaternary sugar surfactant microemulsions (see Fig. 1.9(a)) the phase behaviour of the pseudo-quaternary ionic system can now be represented in a phase tetrahedron if one keeps temperature and pressure constant. 

Graciaa, A., Lachaise, J., Sayous, J.G., Grenier, P., Yiv, S., Schechter, R.S. and Wade, W.H. (1983) The partitioning of complex surfactant mixtures between oil-water microemulsion phases at high surfactant concentrations. /. Colloid Interface Sci., 93,474-486. 

The principal motivation for studying these sugar-based microemulsion glasses came from the observation that water-oil-surfactant mixtures are extensively for nanomaterials synthesis with the central idea of switching dynamic self-assembly into chemically and mechanically stable supramolecular materials. Template polymerisations are classified as synergistic or transcriptive templating depending on whether the template itself participates in the reaction. 

The synergisms of mixtures of anionic-cationic surfactant systems can be used to form middle-phase micro emulsions without adding short-chain alcohols [109, 110]. The surfactants studied were sodium dihexyl sulphosuccinate and benzethonium chloride. The amount of sodium chloride required for the middle-phase microemulsion decreased dramatically as an equimolar anionic-cationic surfactant mixture was approached. Under optimum middle-phase microemulsion conditions, mixed anionic-cationic surfactant systems solubilised more oil than the anionic surfactant alone. Upadhyaya et al. [109] proposed a model for the interaction of branched-tail surfactants (Fig. 8.16). According to this model the anionic-cationic pair allows oil to penetrate between surfactant tails and increases the oil solubilisation capacity of the surfactant aggregate. Detergency studies were conducted to test the capacity of these mixed surfactant systems to remove oil from... 

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